Below him, as if at the end of some remote tunnel, he heard the humming of a vacuum cleaner.

For example, if gravitational waves were observed to propagate slower than c ( the speed of light in a vacuum ), that would imply that the graviton has mass.

When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high.

Hot-cathode gauges can be damaged or lose their calibration if they are exposed to atmospheric pressure or even low vacuum while hot.

Usually, each instance will have a unique name, so that if you have two instances of vacuum cleaners, one might be " vac1 " and the other " vac2 ".

Other types of electron emitters include lanthanum hexaboride () cathodes, which can be used in a standard tungsten filament SEM if the vacuum system is upgraded and field emission guns ( FEG ), which may be of the cold-cathode type using tungsten single crystal emitters or the thermally assisted Schottky type, using emitters of zirconium oxide.

It is not clear if they use air or vacuum brakes.

An atomic mass unit is, for roughly 40 atoms per cubic meter .</ ref > However, even if every single atom and particle could be removed from a volume, it would still not be " empty " due to vacuum fluctuations, dark energy, and other phenomena in quantum physics.

Andries Pretorius filled the leadership vacuum hoping to enter into negotiations for peace if Dingane would restore the land he had granted to Retief.

Philip quickly revived Spanish ambition ; taking advantage of the power vacuum caused by Louis XIV's death in 1715, Philip announced he would claim the French crown if the infant Louis XV died and attempted to reclaim Spanish territory in Italy, precipitating the War of the Quadruple Alliance in 1717.

They must operate in a vacuum with temperatures potentially ranging across hundreds of degrees Celsius as well as ( if subject to reentry ) in the presence of plasmas.

The simplest way to test the weak equivalence principle is to drop two objects of different masses or compositions in a vacuum, and see if they hit the ground at the same time.

In fact adding the cosmological constant to Einstein's equations does not lead to a static universe at equilibrium because the equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion.

Weinberg explains that if the vacuum energy took different values in different domains of the universe, then observers would necessarily measure values similar to that which is observed: the formation of life-supporting structures would be suppressed in domains where the vacuum energy is much larger.

Specifically, if the vacuum energy is negative and its absolute value is substantially larger than it appears to be in the observed universe ( say, a factor of 10 larger ), holding all other variables ( e. g. matter density ) constant, that would mean that the universe is closed ; furthermore, its lifetime would be shorter than the age of our universe, possibly too short for the intelligent life to form.

This argument depends on a lack of a variation of the distribution ( spatial or otherwise ) in the vacuum energy density, as would be expected if the dark energy were the cosmological constant.

There is no evidence that the vacuum energy does vary, but it may be the case if, for example, the vacuum energy is ( even in part ) the potential of a scalar field such as the residual inflaton ( also see quintessence ).

An electromagnetic wave that travels a path of given optical path length arrives with the same phase shift as if it had traveled a path of that physical length in a vacuum.

Glass under vacuum becomes more sensitive to chips and scratches in its surface, as these form strain accumulation points, so older glass is best avoided if possible.

Static discharge from charged toner particles can ignite dust in the vacuum cleaner bag or create a small explosion if sufficient toner is airborne.

The relation between the magnetizing field H and the magnetic field B can also be expressed as the magnetic permeability: or the relative permeability, where is the vacuum permeability.

These processes are important in the vacuum state and renormalization of a quantum field theory.

However, metal electrode surfaces can cause a region of the vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission.

Thermionic emission occurs when the thermal energy exceeds the metal's work function, while field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunneling, which results in the ejection of free electrons from the metal into the vacuum.

These regions may be initiated by field electron emission, but are then sustained by localized thermionic emission once a vacuum arc forms.

In the early cold cathode vacuum tubes, called Crookes tubes, this was done by using a high electrical potential between the anode and the cathode to ionize the residual gas in the tube ; the ions were accelerated by the electric field and released electrons when they collided with the cathode.

Cathodes used for field electron emission in vacuum tubes are called cold cathodes.

The typical example is of two uncharged metallic plates in a vacuum, placed a few micrometers apart as in a capacitor but without any external electromagnetic field.

When this field is instead studied using the QED vacuum of quantum electrodynamics, it is seen that the plates do affect the virtual photons which constitute the field, and generate a net force — either an attraction or a repulsion depending on the specific arrangement of the two plates.

The Casimir effect can be understood by the idea that the presence of conducting metals and dielectrics alters the vacuum expectation value of the energy of the second quantized electromagnetic field.

In the field of high-energy particle physics, the fundamental velocity unit is the speed of light c. Thus, dividing energy in eV by the speed of light in vacuum, one can describe the momentum of an electron in units of eV / c.

Until 1950 this field was called " radio technology " because its principal application was the design and theory of radio transmitters, receivers and vacuum tubes.

switching mixers use arrays of field effect transistors or ( in older days ) vacuum tubes.

Absolute gravimeters, which nowadays can also be used in the field, are based directly on measuring the acceleration of free fall ( for example, of a reflecting prism in a vacuum tube ).

* There are always vacuum fluctuations of the electromagnetic field, according to quantum mechanics.

Schematic representation of a planetary dipole magnetic field in a vacuum ( right side ) deformed by a region of plasma with infinite conductivity.

A magnetic field in a vacuum cannot penetrate a volume with infinite conductivity.

If one assumed that magnetopause was just a boundary between a magnetic field in a vacuum and a plasma with a weak magnetic field embedded in it, then the magnetopause would be defined by electrons and ions penetrating one gyroradius into the magnetic field domain.

The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field.

However, it leads to a fairly simple picture of the vacuum state and is not easily amenable to use in some quantum field theories, such as quantum chromodynamics which is known to have a complicated vacuum characterized by many different condensates.

There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, Planck's constant h, the electric constant ε < sub > 0 </ sub >, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed limit of the Universe and is expressed dimensionally as length divided by time ; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.

Because it retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications, such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles.

This reduction is then compared to the field strength of the charged particle in a vacuum.

If, for example, a pair of atomic nuclei are merged to very briefly form a nucleus with a charge greater than about 140, ( that is, larger than about the inverse of the fine structure constant, which is a dimensionless quantity ), the strength of the electric field will be such that it will be energetically favorable to create positron-electron pairs out of the vacuum or Dirac sea, with the electron attracted to the nucleus to annihilate the positive charge.

The strength of the vacuum is critical in the speed of the drying and therefore the quality of the product.

Care must be taken to produce a vacuum of suitable strength.

While in everyday siphons, atmospheric pressure is the driving mechanism, in specialized circumstances other mechanisms can work – in the laboratory, some siphons have been demonstrated to work in a vacuum – see vacuum siphons – indicating the tensile strength of the liquid is contributing to the operation of siphons at very low pressures.

While water has been found to have a great deal of tensile strength in some experiments ( such as with the z-tube ), and siphons in vacuum rely on such cohesion, common siphons can easily be demonstrated to need no liquid tensile strength at all to function.

Despite these shortcomings, in some situations siphons do function in the absence of atmospheric pressure and via tensile strength – see vacuum siphons – and in these situations the chain model can be instructive.

However, the superior size, physical strength, endurance and resistance to space vacuum of Commander Type Zentradi makes them much more dangerous and equal opponents for the Valkyrie.

Physical properties of refractory metals, such as molybdenum, tantalum and tungsten, their strength, and high-temperature stability make them suitable material for hot metalworking applications and for vacuum furnace technology.

The term " vacuum fluctuations " refers to the variance of the field strength in the minimal energy state, and is described picturesquely as evidence of " virtual particles ".

where is the magnetic field strength, is the speed of light, is the permeability of the vacuum, and

In particular, bumping can often be prevented by taking homogeneous phases into the evaporation, by carefully regulating the strength of the vacuum ( or the bath temperature ) to provide for an even rate of evaporation, or, in rare cases, through use of added agents such as boiling chips ( to make the nucleation step of evaporation more uniform ).

The thick wall of the Büchner flask provides it the strength to withstand the pressure difference while holding a vacuum inside.

Tom Strange is capable of flight ( or at least vast Golden Age Superman-like leaps ), superhuman strength, and surviving indefinitely in the vacuum of space ( without air or water ), and has invulnerability to re-entry, extreme impacts ( falling to Earth from space ) and bullets.

In 1977, George Savvidy showed that the QCD vacuum with zero field strength is unstable, and decays into a state with a calculable non vanishing value of the field.